Manufacture of metallic filaments for incandescence lighting.



UNITED STATES PATENT OFFICE CHBISTOPE HEDQ'BICH OF BERLIN, GERMANY. MANUFACTURE OF METALLIC FILAMEN'I'S FOB INGANDESQENCE LIGHTING.

No Drawing.

Specification of Letters Iate'nt.

Application filed April 20, 1910. Serial No. 556,688.

- Patented Feb. 6, 1912.

To all 'wbomit may concern:

Be it known that I, CHnIs'rorn HEINRICH WEBER, chemist, a citizen of the German Empire, residin at '15/16 Kurfiirstenstrasse, Berlin, ermany, have invented a certain new and useful Improved Manufacture of Metallic Filaments for Incandescence Lighting, of which the following is a specification.

This invention relates to the manufacture of metallic filaments for incandescent lighting, and has for its particular object the production of a filament which is durable, and which on account of its reduced brittleness will stand considerably more shock and jar of transportation than can be withstood by metallic filaments made according to the processes at present used.

According to this invention it is possible to reduce the brittleness of metal filaments made from metals of high melting points, for instance from tungsten. The process is based on the addition to the metals of high melting points, of a metalloid in the form of tellurium. Tellurium is an exceedingly brittle body which can be easily reduced to powder, and vaporizes at 1400 C. It is therefore specially remarkable that such a brittle body, when alloyed in the proper manner with metallic tungsten, should give an exceedingly tough alloy which can be advantageously used 'in the incandescent lamp filament industry. Three methods of manufacturing such filaments, which will be sufiicient for purposes of illustration, may be given briefly as follows:

1. A mixture is made of 11.7 grams of fine tungsten powder and 0.3 of a gram of .purest pulverized tellurium. The mixture is mixed with 2 grams of an organic substance, such as concentrated solution of sugar, and formed in the usual way into filaments and preliminarily heated in a vacuum. This operation is effected by placing the filaments in a porcelain tube which is well evacuated, and the tube is then heated slowly up to 800 C. Thereupon the tube is allowed to cool and the preliminary glowing operation is completed. This preim'inary glowing eflfects the decom ositlon of the organic binding agent adde to the paste and renders the filament conductive. Then follows the forming operation which differs materially from the forming process 5 of ordinary tungsten filaments. The formof the filament is mg is effected by the threads being introduced into a receptacle filled with an inert gas, such as hydrogen, nitrogen, or the like. Then an electric current is caused to pass through the filament, whereby the latter is caused to glow; this heating of the filament 1s continued up to brightest incandescence. During this operation the filament sinters and the single particles are fused together,

whereby the filament receives a metallic surface. It IS however absolutely necessary to form the filament by the dull red glowing operation for a considerable time, in order that the tellurium contained in the mixture of the metals should be carefully melted, and should cement together the single metal partlcles, a tungsten-tellurium alloy being formed at the same time. The temperature thereupon slowly raised to bright red heat, nearly the whole quantity of the tellurium contained'being vaporized from the filament, and only a very small quantity of tellurium, which can be proved only by qualitative analysis, remainmg m the filament, probably about 0.05 per cent. It must be pointed out that in order to make the filaments more elastic, only traces of tellurium are required, since greater quantities of tellurium make the filaments still more brittle than pure tungsten filaments.

2. A mixture of fine powder of metallic tungsten and about 2% of purest pulverized tellurium dioxid is made, and the process carried out for obtaining the filament as stated above. These filaments are then heated at first at dark red heat in an atmosphere consisting of a mixture of a neutral gas, for instance hydrogen, and sulfur dioxid (S0,). The temperature is adually raised to bright red heat, a reduction of the tellurium dioxid by the hydrogen and the sulfur dioxid taking place 1n accordance with the following equation:

Teo,+s0,+H,=Te+H,so,. The pure tellurium is accordingly separated on the filament, slight vapors of sulfuric acid being formed, which however do not affect the quality of the filament. This second method is to be preferred to the first one, as tellurium which is obtained during the same in the nascent state forms the desired tungsten alloy in a much easier and more energetic manner, and the filaments produced are in fact still more elastic than those produced when proceeding according to the first described method.

3. Such filaments can also be obtained by pure tungsten filaments being heated in an atmosphere of tellurid of hydrogen TeH,) and a neutral gas, for instance hyrogen. This method) has, however, the

' drawback that forforming the filament in question, a considerably longer time is required to get favorable results. When treatin pure tungsten metal filaments in the sai gas mixture, tellurium is first separated on the surface'of the metal filaments and penetrates only very slowly into the interi'or of the filament. Special care must be taken that the initial temperature of the filament should not be too hlgh, not higher than 500 C. in order that the tellurium separated should not again vaporize at once on the surface, but that there should be suflicient time for a portion of the tellurium to penetrate into the filament.

It must again be pointed out expressly that the quantities of tellurium to be used are only very small, as otherwise the opposite result will be obtained. The limits within which the addition should be kept are at least 0.02% and at most 1%. The experiments I have made show that those filaments have the best properties in which at the end of the heating operation no quantitative quantity of tellurium could be discovered.

As regards the durability of the filaments and blackening produced by them, it has been found that the results are at least as good as those obtained with pure tungsten laments, although it would seem at first sight that tellurium which vaporizes at 1400 C. ought to be finally separated out of the filament. That, however, does not take place, but the required, very slight traces of the metalloid adhere so firmly to record of the case in the Patent Otfice.

[seam] the tungsten metal that no subsequent separation is produced by calcining in a vacuum. It must be further pointed out that the proportion of carbon in the metallic filaments is also smaller than in the case of ordinary tungsten metal filaments (produced by the Pasteve process), as it appears as if, in the vaporization of tellurium the carbon bound to these metalloids, disappears with them.

What I claim is:

1. A metallic filament for incandescent lighting comprising a metal of high melting point and containingtellurium within the limits of 0.02% and 1.%, substantially as de ment from the mixture, and heating the filament in an atmosphere consisting of a neutral gas and sulfur dioxid.

4. The process of manufacturing metallic filaments for incandescent lighting which consists in mixing finely divlded tungsten with pulverized tellurium dioxid and a suit-' able binder, forming a filament from the mixture, and heating the filament in an atmosphere consisting of a neutral gas and.

sulfur dioxid.

In testimony whereof, I aflix my signature in presence of two witnesses.

CHRISTOPH HEINRICH WEBER.

lrVitnesses ELIsE SOHNOKERT, Gnono FALKERvrrz.

It is hereby certified that inLetters Patent No. 1,010,804, granted February 6, 1912, upon the application of Christoph I'leinrich Weber, of Berlin, Germany, for an improvement in the Manufacture of Metallic Filaments for Incandescence Lighting, an error appears in the printed specification requiring correction as follows:

Page 2, line 62, percentage, for 0.2 read 0.02; V and that the said Letters Patent should be read with this correction therein that the same may conform to the Signed and sealed this 2d day of July, A. D., 1912.

. C. C. BILLINGS,

Acting Commissioner of Patents. 

